Readynas 104 drops out when copying to it

I read somewhere that those parameters are only passed by the mkfs.btrfs command, meaning no conversion is possible, but a little scripting can do the job, creating a new volume, resizing every time it's needed, moving data, updating config, deleting the old volume.
But I don't believe they will do it. First of all because it's risky since it's a long process and everyone has a different configuration (disk size, free space, file naming, file number, snapshots...) meaning every error (or power problem) would cause data loss. And if the NAS locks while copying... The NAS would be unavailable for the time (we don't want to update data while it's copied, do we ? and data already copied won't be available until the volume is mounted in the right place to avoid problems with the web interface ). It will delay the update because of all the testing needed. And since they suggest to reset for any reason, I believe they don't care about the data, so why bother doing a script ?

So I believe you are right, a volume recreation will be needed after the update, either by doing it manually via SSH, or by resetting the NAS.